<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>任何变量都可以通过设置值为undefined来清空,类型为undefined</title>
</head>

<body>
    <p>变量可以通过设置 <b>undefined</b> 来清空。</p>
    <p id="demo"></p>
    <script>
        var person = { firstName: "John", lastName: "Doe", age: 50, eyeColor: "blue" };
        var person = undefined;
        document.getElementById("demo").innerHTML =
            person + "<br>" + typeof person;
    </script>
</body>

</html>